Mattis is studying Philosophy and Political Science in a combined bachelor's program at Freie Universität Berlin. His academic interests particularly focus on AI ethics, international economics, and the study of autocracies.
Before his employment at the Center for International Relations, Mattis completed an internship in the Department of 'Institutions and Political Inequality' at the Berlin Social Science Center (WZB).

In the Center for International Relations, Mattis supports both research on international norms and teaching.